1. Field of the Invention
The present invention relates to a magnetic random access memory (MRAM) in which a memory cell is constructed using MTJ (Magnetic Tunnel Junction) elements having xe2x80x9c1xe2x80x9d, xe2x80x9c1xe2x80x9d-information stored therein by a tunneling magneto resistive effect.
2. Description of the Related Art
In recent years, there have been proposed many memories having information stored therein by new methods, and one of them is the tunneling magneto resistive (hereinafter, denoted as TMR) effect proposed by Roy Scheuerlein et. al. (for example, refer to ISSCC2000 Technical Digest p. 128 xe2x80x9cA 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each cellxe2x80x9d).
The magnetic random access memory stores xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d-information by the MTJ elements. The MTJ elements have a structure in which an insulation layer (tunnel barrier) is sandwiched with two ferromagnetic layers. The information stored in the MTJ elements is determined by whether or not the orientations of spins of the two ferromagnetic layers are parallel or anti-parallel.
Here, parallel means that the orientations of the spins of the two ferromagnetic layers are the same, and anti-parallel means that the orientations of the spins of the two ferromagnetic layers are opposite to each other.
Generally, one of the two ferromagnetic layers constructing the MTJ element is a pin layer in which the orientation of the spin is pinned. When xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d-information is stored in the MTJ elements, the orientation of the other one (free layer) of the two ferromagnetic layers is varied according to written information.
A magnetic random access memory according to a first aspect of the invention comprises: an array having a plurality of MTJ elements accumulated in a plurality of portions; first conductive lines arranged in the array; first elements connected to the first conductive lines; second conductive lines arranged in the array which have the same function as that of the fist conductive lines and are arranged above the first conductive lines; and second elements connected to the second conductive lines, wherein the number of MTJ elements arranged in at least one portion of the plurality of portions is larger than the number of MTJ elements arranged in each portion lower than the portion, and the first and second elements are arranged immediately below or on the periphery of the array.
A magnetic random access memory according to a second aspect of the invention comprises: an array having a plurality of MTJ elements accumulated in a plurality of portions; first conductive lines arranged in the array; fist elements connected to the conductive lines; second conductive lines arranged in the array which have the same function as that of the first conductive lines, and are formed above the first conductive lines; second elements connected to the second conductive lines, wherein the first and second elements are both arranged on the periphery of the array but immediately below the array, and the first elements are arranged nearer to the array than the second elements.